Coaxial-line switch



Dec. 8, 1953 J. A. NELSON 2,662,142

IIIIIIIIIIIIIIII CH ,mil WWW! @Mimi-imi fjW/wunW-S "mw 7 Mn/MUM W Patented Dec. 8, 1953 COAXIAL`LINE SWITCH Jessie Ann Nelson, New York, N. Y.assignor to the UnitedStates yofulimerica as represented by the-Secretary of the Army Application November 3, 1950, Serial No. 193,836

(Cl. 20D-153) 12 Claims.

This invention relates to improvements incol-V axia'l-line switches.

Examples of coaxial-line switches over which the disclosed embodimentof'the presentY invention is considered to-have one or more important advantages, are describedfin Patent No. 2,427,940', issued September 23, 1947, to Jay'J. Ayres, in

Patent No. 2,426,186, issued August 26; 1947, to-

Orville E; Dow., and-onpages 528 to 533v in vol; 9 of the Massachusettslnstitute ofV Technology Radiation Laboratory Ser-ies, published 1948 by the McGraw-Hill Book.v Company, Inc;

Among the'objects ofthe invention isthe provisionof an improved coaxial-line switch of the character referred to, which can function eiii ciently asa single-pole, double-throw switch in coaxial-transmission-line applications at' any frequency, and with-whichitispossible to switch current between two coaxial lines-without aiect-A ing the -standing-waveratio existing on-theY-fe'ed or input line.

Other objects and advantages will hereinafter appear.

In. accordance withl the present invention, a coaxial-line switch isso designedf that the characteristicimpedance of the coaxial line forming the switch is constant throughout, without discontinuities except at a right-anglev turn, at which point the discontinuity is of' the same order of magnitude asthat found in a right angle adapter or in. any 90 bend. Thus, the only sources of' standing-Wave ratio-distortion are in the' 90? bend and'Y in the connectors themselves. The: improved switch', accordingly, will not disturb the sta.nding.-wave ratio on a coaxial line tov any appreciable extentv at any: frequency, where a type-Niconnector'may beused.

For the purpose` of; illustrating; the invention, an'embodiment-thereof is shownrin thedrawing, wherein:

Fig. 1 is a View partly in section. andl partly.l

broken away, of a coaxial-line switch` constructed and havingl operating characteristics in accord.h ance with the invention, the section being taken on theline -I-I in'Fig. 2;

Fig. 2-is a, plan view, partly iny section, of the improved switch, the section being'taken onthe line 2-2 in Fig. 1; and

Figs. 3 and 4 are enlarged, detail, sectional views, the sections being taken on the' lines 3 3 and 4--4, respectively, in Fig. 1.

In the drawing, the reference numeral ID designates the switchV casing to which are` secured type-N coaxial-line connectors il, I2y and I4 ofl a. conventional construction; The connectors Il and I2 provide, respectively, means for connecting two-coaxial output lines to theswitch, and the connector I4 provides means for connecting a coaxial input line to the switch.

With the switch installed, the coaxial input lineforms the stem of a T and'may be connected se-y lectively to the coaxial output lines which form the aims of the T. For this purpose, switch elements inthe form ofrelatively short' sections I5 and I6 of the inner conductors of the respective arm-s of the T, are supported for movement into and out of Contact with the complementary section or inner conductor I la of the stem of the T. The outer conductors of the three transmission lines connected into the switch, are connected permanently through the switch casing I e which is of electrically-conductive material.

The inner section or inner conductor Ma of the stem of the Textends through and is sup-- ported by the dielectric insert I 4b of connector I4?. The respectiveinner sections or inner conductors Ila and I2afof the arms ofthe T likewise extendr through and are supported by the dielectric .inserts IIb and |21), respectively, of connectors II and I2.

Parts IIJa and IDb constitute, in effect, part of thelouterconductor, and have a sliding t with respect to each other and 4with respect to the casing I0. Theinner-conductor section I5 is attached rigidly to part IDa by pins I5a of dielectric material. Thediameter of the central portionsV |512V of these pins is made greater than that of the ends, whereby the central portions I5b serve as spacers. Similarv pinsV I 5a of dielectric material' serve to attach the inner-conductorsection I6 rigidly to the part lub.

The inner-conductor sections or switch elements I5 and I6- are moved manually, orA by any conventional control mechanism, into one or the other of two positions by studs Hand I8- screwed, respectively, into the parts Ia and Illb and' extending through and having a sliding t with respect to a cover plate I9 secured to casing I.

Withsection I5 in the full-line position shown, and with section I6 in the fully-retractedv or uppermost position indicated by dash lines, in Fig. 1, the output line screwed toA connector I2 will be disconnected from the input line screwed to connector I4, whereas theoutput line screwed to connnecter II will be connected to this input line. With the inner section I5 raised and the inner section lli` lowered, however, the output line screwed to connector II willbe disconnected fromtheinput line, and the latter willbeconnected with the output line screwed to connector l2. From this it will be seen that the improved coaxial-line switch can function as a single-pole, double-throw switch in a coaxial-transiniA online system. In other` words, the transmission line forming the stein of the T may be switched alternately between the two transmission lines forming the arms of the T.

The inner-conductor sections Ila, 12a, 4a, l5 and IE have a circular cross-section, and their respective ends are tapered, as shown. The switch-end of the inner-conductor section Ida is tapered on both sides, symmetrically with respect to its longitudinal axis, the angle of the taper being substantially 6dr. The angle of taper is the same for the other contact surfaces. Just a straight slice for the taper, at any chosen angle, would cause a relatively large discontinuity at the lioint, since the T-arrns l5 and I6 would have elliptical faces, and the T-stem Ida would, in such case, have two half-elliptical faces. Such discontinuity at the joint is reduced, as shown more clearly in Figs. 3 and 4, by V-grooves Hic in the tapered contact faces of bar I5. Similar grooves are made in the tapered contact faces of bar It, and the respective tapered contact faces of sections lid and 12a are V-shaped to nt or correspond. In other words, the V-groove faces are concave at the ends of the T-bars or movable switch elements l5 and I6, and are convex at the top of the T-stem ifi-a and at the inwardly directed ends of the inner conductor sections llc and 12a. Another advantage of this V-groove or vl-shaped construction is that it makes the movable T-bars l5 and I self-aligning when they are pushed inwardly into the casing I to engage the complementary contact faces of the sections Ila, lila and ldd. The angle of the V-groove or V-shape determined for the best matching of the two faces, shown in Fig. 4.

With the parts of the improved switch in the respective positions thereof shown in Fig. l, the inner-conductor section or bar l attached to the movable outer-conductor section ica, is in contact with the inner section or T-stem Illa and with the inner-conductor section l la of the type- N connector Il. Also, the cuter-conductor section IGa is in -position to form a continuous outerconductor surface with the permanent parts comprising the wall of casing l0, and the outer-conductor section b and the inner-conductor section or T-arm l 6 attached to the latter, are ccmpletely withdrawn into the wall of casing Il).

With the stud Il pulled out and the stud I8 i pushed in, the conditions are vice Versa. It will therefore be seen that of the two bars i5 and IB, the one which is not in use is recessed into the outer-conductor wall of the casing, and thus is grounded (at least capacitatively for R. F. frequencies). By means of this arrangement and operational feature, possible capacitive feedthrough due to the proximity of the unused T-bar, is avoided.

When either of the two, movable switch units is in contact position, the characteristic impedance of that portion of the transmission line is undisturbed. In other words, the improved switch is so designed that the characteristic impedance of the coaxial line is constant throughout, without discontinuities except at the rightangle turn. At that point, the discontinuity is of the same order of magnitude as that found in a right-angle adapter or in any 90 bend. Thus, the only sources of standing-wave-ratio-distortion are in the bend and in the connectors themselves, and the switch will not disturb the standing-wave ratio on a coaxial line to any appreciable extent at any frequency, where a type-N connector may be used.

For a particular application of the invention, it might be more expedient or advantageous to shape or otherwise design casing l0 and associated parts so that there is a Y-joint at the center, instead of the arms I5 and I6 and the stem 14a being disposed as disclosed herein, to form a. T- joint.

A structural feature which is considered to be important, resides in the arrangement and combination of parts whereby the center-conductor connection is made right at the stem-joint so that no metal stub remains to change or disturb the standing-wave ratio, as is the case in some of the designs proposed heretofore. For example, some of the prior switches have a stub on the inner stem of the T-joint so that there can be an undesirable capacitance to the unused arm. This capacitance is determined by the distance between the inner end of the T-stem and the unused arm, and this distance can be greater in a switch of the present construction than has been practical with the switches having stubs on the T-stem.

One of the broader aspects of the invention embodied in the construction disclosed, resides in the provision of a single-pole, double-throw concentric coaxial-line radio-frequency switch constructed in the form of a T or Y, and wherein either of two sections of the inner conductors of the arms can be withdrawn completely into the wall of the switch when not in use, thus leaving a transmission line with no discontinuities other than a right-angle or obtuse-angle bend. Aside from its function as a coaxial-line switch, it is feasible that the device could be used, as well, as a T-junction or as a Y-junction.

An additional reason why the unused arm in the improved switch introduces less disturbance than has been the case in prior constructions, is because when one of the center conductors I5 and I6 is withdrawn, the associated outer-conductor section lea or Ib to which it is rigidly attached acts like a wave-guide. The cut-olf frequency for this wave-guide can be made higher than the highest operating frequency.

The improved switch can operate over a very wide frequency range, i. e., substantially megacycles or less, to 4,000 megacycles. It provides, furthermore, a fairly good impedance match over this large frequency range, and the standing-wave ratio is relatively low. The upper frequency limit is determined by the connections to the lines and also by the Wave-guide consideration above referred to. The lower frequency limit is determined by the contact joints in the inner conductor.

While but one, and a preferred embodiment of the invention has been disclosed, it will be understood by those skilled in the art that various modiiications, such as in the size, shape and arrangement of the parts, may be made without departing from the spirit of the invention or the scope of the claims.

The invention claimed is:

l. In a coaxial-line switch of the character described, a casing, a pair of coaxial-line connectors fixed with respect to said casing and each provided with an inner-conductor section, a third coaxial-line connector fixed with respect to said casing and provided with an inner-conductor section and disposed intermediate said first-named connectors; and switch= elements supported by and for movement with respectto said casing and withz respect to each other into. and out of ccntact with said third-named section and with one of said first-named sections to connect said thirdnamed section with either of the latter selectively, the inner wall portion of said casing forming in association with any combination of said three sections the outer-conductor or" a coaxial transmission line, each of said switch elements being shaped and disposed for substantially complete withdrawal into the wall structure of said casing when in position out of contact with said thirdnamed section, the longitudinal axes of said rstnamed connectors being disposed in nonparallel relation with respect to the longitudinal axis of said third connector, said first-named connectors being directed respectively in opposite directions from the longitudinal axis of said third connector.

2. In a coaxial-line switch of the character described, a conductive casing, coaxial-line connectors fixed with respect to said casing and each provided with an inner-conductor section, a conductive part movable with respect to said casing, a switch element, and means of dielectric material attaching said element to and spacing said element from said part for movement into and out of contact with said sections, said element being shaped and disposed for substantially cornplete withdrawal into the wall structure of said casing when in position out of contact with said sections.

3. In a coaxial-line switch of the character described, a conductive casing, a pair of coaxialline connectors xed with respect to said casing and each provided with an inner-conductor section, a third coaxial-line connector fixed with res-pect to said casing and provided with an innerconductor section and disposed inte-rmediate said first-named connectors, outer-conductor sections supported by and for movement with respect to said casing and with respect to each other, -switch elements, and means of dielectric material attaching said elements respectively to and spacing said elements respectively from said parts for movement into and out of Contact with said third-named section and with one oi said first-named sections to connect said third-named section with either of the latter selectively, each of said outer-conductor sections and the respective switch element fixed thereto and spaced therefrom being shaped and disposed for substantially complete withdrawal into the wall structure of said casing when in position to place the switch element out of contact with said thirdnamed section.

4. In a coaxial-line switch of the character described, a casing, a pair of coaxial-line connectors xed with respect to said casing and each provided with an inter-conductor section, a third coaxial-line connector fixed with respect to said casing and provided with an inner-conductor section and disposed intermediate said rstnamed connectors, and switch elements supported by and for movement with respect to said casing and with respect to each other into and out cf contact with said third-named section and with one of said first-named sections to connect said third-named section with either of the latter selectively, the inner end of said third-named section being tapered and substantially V-shaped on opposite sides thereof, both ends of each of said switch elements being tapered and provided with a V-groove.

5; In'acoaxial-line switch of `the-character described, a conductive casing, coaxial-line connectors flxedwith respect to said casing and each provided withan inner-conductor section, a conductive part movable to a retracted position within thewall structure of said casing and to a forward position to constitute part of the inside surface of said casing, a switch element, and means of dielectricV material attaching said element to4 and spacing'said element from said part for movement into and out of contact with said sections, said element being shaped and disposed for retraction with said part into said Wall structure.

6, In a coaxial-line switch of the character described, a casing, a pair of coaxial-line connectors fixed with respect to said casing and each provided with an inner-conductor section having a circular cross-section, a third coaxial-line connector fixed with respect to said casing and provided with an inner-conductor section having a circular cross-section, said third connector being disposed intermediate said first-named connectors, and switch elements each having a circular cross-section and supported by and for movement with respect to said casing and with respect to each other into and out of contact with said third-named section and with one of said iirst-named sections to connect said third-named section with either of the latter selectively, the inner end of said third-named section being tapered and substantially V-shaped on opposite sides thereof, both ends of each of said switch elements being tapered and provided with a V- groove.

7. In a coaxial line switch, a pair of switch contacts for the center conductor of said line, one contact having a V-shaped wedge and the other contact having a V-shaped groove shaped to flt said wedge.

8. In a coaxial line switch as set forth in claim 7, the line defining the bottom of said V-shaped groove being at an angle of 64 with the axis of said coaxial line.

9. In a coaxial line switch, a center conductor of said coaxial line having a tapered end which is V-shaped on opposite sides thereof, the line defining the bottom of each V of said end being at an angle of 26 with respect to the center axis of said center conductor, a first switch arm having a V-grooved end shaped to fit one side of said tapered end, a second switch arm having a. V- grooved end shaped to t the other side of said tapered end, and means for engaging and disengaging the grooved ends of said arms with the tapered end of said center conductor.

10. A coaxial line switch comprising a pair of spaced coaxial line sections, a conductive rod forming an arm of said switch, proximate ends of the center conductors of said sections being wedge-shaped, said rod having a length suiiicient to permit simultaneous engagement of the ends thereof with the ends of said center conductors, and means for engaging said rod with and disenaging said rod from both said center conducors.

1l. A coaxial line switch comprising a pair of spaced coaxial line sections, a conductive rod having a diameter approximately equal to that of proximate ends of the center conductors of said sections forming an arm of said switch, said proximate ends being V-shaped, said rod having V-grooved ends shaped to fit respective ones of said V-shaped ends, said rod having a length sufcient to permit simultaneous engagement of the ends thereof with the ends of said center conductors, and means for simultaneously engaging said rod with both said center conductors and simultaneously disengagng said rod from both said center conductors.

12. A switch according to claim 11, in which the axes of said center conductors are at an angle with respect to one another.

JEssIE ANN NELSON.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,406,122 Young Aug. 20, 1946 5 2,426,186 Dow Aug. 26, 1947 2,498,907 Atwood et al. Feb. 28, 1950 OTHER REFERENCES Abstract of Wahl application S. N. 632,584, 16 published April 4, 1950. 

